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Using a photon, physicists have managed to simulate quantum particles traveling through time. Studying the photon’s behavior could help scientists understand some inexplicable aspects of modern physics.

“The question of time travel features at the interface between two of our most successful yet incompatible physical theories — Einstein’s general relativity and quantum mechanics,” University of Queensland’s Martin Ringbauer says in a news release. “Einstein’s theory describes the world at the very large scale of stars and galaxies, while quantum mechanics is an excellent description of the world at the very small scale of atoms and molecules.”

Time slows down or speeds up depending on how fast you move relative to another object. Einstein’s theory suggests the possibility of traveling backwards in time by following a space-time path that returns to the starting point in space — but at an earlier time. This is called a closed timelike curve (pictured above). It’s a traversable wormhole.

In a quantum regime, the authors say, the paradox of time travel can be resolved, leaving closed timelike curves consistent with relativity. Near a black hole, for example, the extreme effects of general relativity play a role.

Pictured above, a space-time structure exhibiting closed paths in space (horizontal) and time (vertical). A quantum particle travels through a wormhole back in time and returns to the same location in space and time.

“The properties of quantum particles are ‘fuzzy’ or uncertain to start with, so this gives them enough wiggle room to avoid inconsistent time travel situations,” UQ’s Tim Ralph explains. “Our study provides insights into where and how nature might behave differently from what our theories predict.” These include the violation of Heisenberg’s uncertainty principle, cracking of quantum cryptography, and perfect cloning of quantum states.